Utilities, such as those providing electric, gas, water and telephone service, often bury their conveyances (i.e., pipes and/or cables) underground for reasons of safety and aesthetics. Usually, the environment and terrain dictate the type of method employed for burying such conveyances. In rural areas, utilities prefer direct burial which they accomplish by plowing or trenching the earth. In urban environments, and when crossing waterways, boring is preferred. To complete such a boring operation, the utility, or a contractor under its employ, first excavates a pit at each of the opposite ends of the intended route for the conveyance. From the one pit, a boring machine (auger) forces a boring head horizontally through the earth into the other pit to create a tunnel through which a utility conveyance can pass.
Underground utility conveyance burial by boring does create a certain risk. An operator must carefully control the path of the boring head to avoid contact with one or more existing underground utility conveyances buried in proximity to the path created by the boring head. For this reason, many utilities, such as AT&T, have regulations governing the minimum allowable distance permitted between the boring head and an existing underground utility conveyance. To facilitate control of the boring head, most boring head manufacturers provide a transmitter (hereinafter referred to as a "sonde") in the boring head for transmitting a signal in the range of 33 Hz. to 9 kHz. The signal transmitted by the sonde radiates through the ground for detection by one or more receivers located above ground. By monitoring the signal radiated by the sonde in the boring head, the operator of the boring machine determines the relative position of the boring head as it bores a path through the earth to avoid contact with an existing underground utility conveyance.
Unfortunately, the signal radiated by the sonde head tends to induce electromagnetic signals in other facilities, such as other underground utility conveyances, causing one or more of them to radiate signals in the vicinity of the conveyance of interest. The receiver(s) tuned to receive the signal radiated by the sonde also receive the signals induced in, and radiated by, such other facilities, causing confusion regarding the actual position of the boring head. Since many boring operations occur in close proximity to existing underground utility conveyances, an error in determining the relative position of the boring head can prove disastrous. Indeed, boring operations have damaged existing underground conveyances, leading to service outages and lost revenues, not to mention the cost associated with repairs.
Thus, a need exists for providing an alert when a boring head lies within the minimum allowable distance from an existing underground utility conveyance, thereby avoiding damage to the conveyance